Existing honing machines normally control the beginning of the honing cycle wherein the feed system is rapidly expanding the tool to a specific feed position. If the system expands the tool too far or too fast it risks the chance that the abrasive will impact the workpiece or bore surface with too much force and thus damage the tool and/or fixture. If the system doesn't expand the tool far enough such that the abrasive does not touch the bore surface, or if it expands too slowly, then the machine will hone air and unnecessarily increase the honing cycle time.
A common known compromise to this challenge of balancing the maximum starting feed position, and feed rate at the beginning of the honing cycle is to rapidly expand the tool to some known position less than the minimum expected location of the bore surface. One basic disadvantage of this method comes up if the starting diameter of the un-honed work piece varies from work piece to work piece. Under these conditions the system could still waste cycle time by honing air between the positions that the tool had rapidly expanded out to, to the actual position of the bore wall.
Reference in regard to known feed systems, U.S. Pat. No. 3,849,940 (Yoshino et al., Honing Machine) which describes a feed system that contains both a constant force and a constant rate system mechanically coupled in such a way that the faster of the two systems will control the expansion of the honing stones. However, if the constant rate system is in control, then there is no means to measure feed force or to correct bore errors caused by variances in feed force. Also, it is not possible to select the slower system when it is desirable to do so, e.g. to improve bore geometry at the end of the honing cycle.
U.S. Pat. No. 4,187,644 (Fitzpatrick, Dual Feed Apparatus for Multiple Spindle Honing Machine) describes a feed system where a cylinder (constant force system) expands stones to the point where they contact the workpiece bore and then the feed control switches to a constant rate mechanism. However, this system includes no means to measure feed force or to correct bore errors caused by variances in feed force. Also, it is not possible to select the controlled force system other than for the initial rapid expansion of the stones.
U.S. Pat. No. 4,397,658 (Vanderwal, Feed Control For Honing or Like Machines) describes an oil damper device to provide a slower initial feed rate or even a constant feed rate for the entire honing cycle. However, this includes no means to measure feed force or to correct bore errors caused by variances in feed force.
U.S. Pat. No. 4,679,357 (Richter et al., Method and Apparatus for Displacing a Honing Tool) describes a feed system where a low value torque limit is imposed on a feed motor control so that stones may feed initially very fast up to the point of contact with the bore, and thereafter a higher torque limit is allowed for honing. The torque limit of the motor is roughly equivalent to a limit on feed force, although mechanical inefficiencies limit the accuracy of using of torque limits as feed force limits. This system also does not include a means to measure feed force or to correct bore errors caused by variances in feed force. There also appears to be no means to control the honing feed to a desired feed force apart from merely preventing the force from exceeding some limit.
European Pat. No. 0081383 (Fox, Improvements Related to Honing) claims a control system that uses feedback from a means for monitoring feed position and velocity and a means for monitoring feed force. However, the details of the patent describe only a hydraulic feed system with a position encoder. In such a system, feed force is inferred by measurement of hydraulic pressure and subject to errors such as that induced from frictional forces between the hydraulic piston and its bore. Although the patent refers to means for monitoring force and position, the use of an electronic load cell to directly measure feed force is not mentioned.
European Pat. No. EP 0 575 675 B1 (Grimm, et al, Method and Machine for Finishing a Bore in a Work Piece) uses a feed force measuring device but only for the purpose of determining the target end point (final encoder position) for the honing process by expanding the honing tool into a size-calibrated ring with a feed force equivalent to that measured on the previously finished workpiece. In a limited way this compensates for errors caused by the elasticity of the workpiece and the feed system components, but as the compensation is a static correction based on force measurements in the previous workpiece, it describes no means to dynamically correct for variations encountered with the workpiece currently being honed. It relies on the assumption that every workpiece is virtually identical to the previous workpiece in regards to hardness and the amount of material to be removed. However, in most applications, this assumption cannot be made reliably. Also, this method makes no suggestion that honing feed force can be controlled throughout the honing cycle.
What is generally sought therefore, is to determine and utilize a set of conditions that will optimize the cutting action of a honing tool, particularly the abrasive element or elements thereof, e.g., the honing stone or stones. Specifically, it is desired to optimize the attritive, chemical, and fracture wear process in honing such that the abrasive grit size, concentration, and type, in concert with morphology of the carrier material as a function of material removed, can be adjusted. It is further sought to provide a capability for dressing of the abrasive surface in a manner that assures a repeatable initial condition of the abrasive as a honing cycle commences. To achieve these, what is further sought is a system and method of rapidly advancing the honing tool such the abrasives of the honing tool make contact with the bore surface at a fast rate, without risking damage to the tool, workpiece, honing machine, or operator, while still maintaining bore geometry.